Patent GB-517826-A (GB)
Title: Improvements in or relating to navigation aiding radio systems
IPC: G01S1/02
Filed: 1938-08-06
Abstract: 517,826. Directive wireless systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Aug. 6, 1938, No. 23293. Convention date, Sept. 24, 1937. [Class 40 (v)] In a radio position-finding system comprising two synchronous rotating-beam transmitters and a cathode-ray tube indicator at the receiver, the cathode rays are focused at points on the screen corresponding to the known position of the transmitters and are rotated in synchronism with the rotating beams. When the rotating beams are directed on to the receiver, the rotation of the cathode rays is momentarily stopped, and the rays are focused on to the said points, the intersection of the consequent radial traces indicating the position of the receiver. The transmitters also radiate omni-directionally at the same frequency as the beam transmissions, synchronizing signals being transmitted by interrupting the radiation when the beam is in certain directions, e.g., north, and course-marking signals being transmitted from one transmitter by increasing the radiation when the beam is directed towards the required destination. In the receiver output, the synchronizing signals consequently appear as negative impulses and the marking and beam signals as positive impulses; since the increased field strength due to the synchronizing signals is less than that due to the marking signals, the beam impulses are of greater magnitude than the marking impulses. A double-gun cathode-ray tube may be used, each ray being controlled by the signals from one transmitter, or the ray of a single-gun tube may be alternately controlled by the signals from the two transmitters. The latter type is shown in Fig. 4, in which the cathode ray is alternately focused by the coils 73 operated by commutators 65, 67 on points 23, 25 on the screen 1, Fig. 2, which are adjusted by potentiometers 69 to correspond with the positions of the transmitters " A," " B " as shown on the transparent map 15 adjustably mounted over the screen. Signals of differing radio-frequency from the two transmitters are received on the aerial 41 and separated in the intermediate-frequency amplifiers 49, 51, the audio-frequency outputs from amplifiers 53, 55 being alternately connected to the indicator by commutator 61. The negative synchronizing impulses are fed through amplifier 75 to control the frequency of the relaxation oscillator 77, the output of which is filtered at 79 to give a sinusoidal current which is fed to the phasing inductances 87 and capacities 89 giving dephased potentials which are applied to the deflecting plates 97 of the cathode-ray tube 95 causing the ray to alternately rotate in synchronism with the beams about the points 23, 25. The grid 99 of the tube is normally biased to give a very-low-intensity cathode-ray so that no circular trace is observed. On receipt of a beam signal, the positive impulse is fed to the grid of the valves 113, 115 which are normally biased to cut-off. The anodes of valves 113 and the cathodes of corresponding valves 115 are connected to the deflection plates 97, so that when the valves become conductive on receipt of the signal the deflection plates 97 are earthed and the cathode rays collapse to their centres 23, 25 along the radial lines 33, 35, the intersection of which indicates the position of the receiver. The beam impulses are also applied to the grid 99 of the cathode-ray tube reducing the bias and so increasing the ray intensity as to make the traces 33, 35 on the screen visible. The coursemarking impulses are not of sufficient amplitude to make the valves 113, 115 conductive, but they do increase the cathode-ray intensity sufficiently to make the trace visible, resulting in a mark 29 on the screen in the direction of the required destination, e.g., "Camden" from the transmitter "A" radiating the marking signal. As the receiver moves out of range of the transmitters, the map may be moved to a new position and the cathoderay re-focused by a switch which also tunes the receiver to the next pair of transmitters. In adapting the system to indicate the position of the aeroplane at a fixed land station, the plane transmits impulses on receipt of beam signals which are picked up at the land station together with the beam signals. If the radio beams are rotated in a vertical plane, the system may be used to give vertical guidance in a landing system.